Polyolefins are a class of polymers derived from simple olefins. Known methods of making polyolefins involve the use of Ziegler-Natta polymerization catalysts. These catalysts polymerize olefin monomers using a transition metal halide to provide a polymer with various type of stereochemical configuration.
One type of Ziegler-Natta catalyst system comprises a solid catalyst component, constituted by a magnesium halide on which are supported a titanium compound and an internal electron donor compound. In order to maintain high selectivity for an isotactic polymer product, internal electron donor compounds must be added during catalyst synthesis. The internal donor can be various types. Conventionally, when a higher crystallinity of the polymer is required, an external donor compound is also added during the polymerization reaction.
During the past 30 years, numerous supported Ziegler-Natta catalysts have been developed which afford a much higher activity in olefin polymerization reactions and much higher content of crystalline isotactic fractions in the polymers they produce. With the development of internal and external electron donor compounds, polyolefin catalyst systems are continuously renovated.
The general production scheme for MgCl2 supported catalysts includes a process to make MgCl2 support, impregnation of TiCl4 and Lewis base, and internal donor to the MgCl2 surface. One of the methods of MgCl2 supported catalyst preparation is the reaction of Mg(OR)Cl or Mg(OR)2 with excess TiCl4 diluted in aromatic or halogenated solvents. In such a case, MgCl2 support is formed from the reaction between the magnesium compound and TiCl4 and the internal donor is added to the process during or after the precipitation of the solid support.
In another method, the alkoxy magnesium complex reacts first with electron donor precursor and then with TiCl4. In this process, the electron donor precursor is converted to the desired internal donor during the formation of MgCl2.
In another method, the solid MgCl2 is used to prepare the MgCl2 catalyst. The solid MgCl2 is dissolved in suitable solvents such as alcohol. The solution is then treated with TiCl4 to precipitate the supported MgCl2 catalyst. For example, MgCl2 can be dissolved in hot ethanol and precipitated in cooled hexane in presence of tetraethylorthosilicate (TEOS).
U.S. Pat. Nos. 6,376,417, 4,784,983 and 4,861,847 describe a catalyst system for use in olefinic polymerization prepared by dissolving a halide of magnesium in a solvent system consisting of an organic compound, an organic phosphorous compound and an inert diluent to form a homogenous solution; mixing the homogenous solution with a halide of titanium to form a mixture; precipitating a solid from the mixture in the presence of an auxiliary precipitant; treating the solid with a polycarboxylic ester to load the ester on the solid; and treating the ester loaded with the halide of titanium and the inert diluent.